A piston ring used in an internal combustion engine of an automobile or the like is provided in, for example, a ring groove of an outer circumferential surface of a piston and has a sealing function of inhibiting oil on an inner wall of a cylinder from entering a combustion chamber side from a crankcase side (oil-up) and inhibiting blow-by gas from entering the crankcase side from the combustion chamber side. As a piston ring having such a sealing function, there is a piston ring disclosed in, for example, Patent Literature 1. The conventional piston ring is used as a second ring of an internal combustion engine, and has an inclined surface provided on an upper surface side of an outer circumferential surface and inclined so as to protrude in a radial direction, and an abutment surface provided from a lower end of the inclined surface and coming in sliding contact with a cylinder inner wall.
In addition, in a piston ring disclosed in Patent Literature 2, a thickness of a portion of a body positioned on an opposite side of a joint section is greater than the other portions. The piston ring has a shape close to an ellipse in a state (force-free state) in which a force is not applied in an in-plane direction of the body. In Patent Literature 2, in a state in which the body is placed on a table and a joint gap is closed to a dimension at the time of use, a two-axis difference (d2−d1) between a diameter d1 in a first axis direction passing through a central position of the joint section and a diameter d2 in a second axis direction orthogonal to the first axis direction is negative.